Type II Diabetes (T2D) is a debilitating disease that afflicts an ever-growing population throughout the world. In addition to obesity and insulin resistance contributing towards the development of the disease, beta cell dysfunction is increasingly implicated in promoting T2D. The reduction or loss of beta cell function due to a shift in the cellular state has reemerged as a contributor to disease. The mature state of the beta cell can be perturbed due to exposure to distinct stressors, and this results in loss of cellular identity or de-differentiation. Numerous studies in rodent models have recently reported the occurrence of beta cell de-differentiation that then leads to diabetes. Significantly, T2D patient samples also have been reported to have a perturbation in the expression of key factors that are required for the maintenance of a fully functional beta cell. Identifying mechanisms that perturb the beta cell state that then contributes to the loss of glucose homeostasis is the overarching goal of this proposal. Complex mouse models that regulate gene expression in beta cells provide preliminary evidence of a modified beta cell identity, i.e. a loss of canonical beta cell genes and activation of genes normally absent from a fully functional beta cell. In two mouse models (depletion of the von Hippel Lindau (VHL) gene and activation of the Sox9 transcription factor), erroneous activation of signaling pathways leads to beta cell de-differentiation and diabetes. Probing these transgenic tools allows for further exploration of the components downstream of these regulatory proteins that impact beta cell fate and function. The experiments outlined in this proposal focus on characterizing changes that occur in the pancreatic beta cells in both these mouse models, and validating the results in beta cells that we can now successfully generate from human embryonic stem cells (hESCs) using directed differentiation protocols. We have already conducted preliminary experiments and obtained data to support the hypothesis that novel factors dysregulated in -cells of the mutant animals can perturb beta cell identity and consequently function when expressed erroneously. In addition, we have generated a third model in which we observe -cell dysfunction caused by changes in the metabolic state of the cell, independent of de-differentiation defects. Thus, we have models in place to dissect different modulators of -cell dysfunction. State of the art combinatorial approaches combining the use of transgenic animals, hESC derived -cells, and human islets and -cells, will be employed to characterize the function of these factors in -cell dedifferentiation, metabolic defects, and dysfunction. Candidate factors will be tested for erroneous expression in samples isolated from T2D patients provided by nPOD. The overarching goal of these studies is to identify novel disruptors of -cell function whose activity could be modulated with the intent of preventing or reversing the compromised beta cell state back to a fully functional one in human patients.